The technological importance of thin films has led to the development of a variety of deposition methods.
Chemical vapor deposition (CVD) produces a solid film on a substrate surface by thermal activation and surface reaction of gaseous reagents which contain the desired constituents of the film. Energy required to pyrolyze the reactants is supplied by heating the substrate. For reasonable reaction rates the substrate is heated to relatively high temperatures in the range of about 5000 to 2000.degree. F. degrees. These temperatures preclude application of the process to heat sensitive substrate materials.
Plasma enhanced chemical vapor deposition (PECVD) supplies energy to the reactants by an electrical discharge in a gas which forms a plasma in the deposition chamber. Generally the substrate is immersed in the plasma. The deposition rate is usually low.
Polycarbonate is often the engineering material of choice for glazing and optical applications because of its high impact strength, low density, optical clarity, and good processibility. However, the polycarbonate material is soft, lacks glass-like abrasion resistance, and is sensitive to temperatures above about 300.degree. F. Prior work had shown that a silicon oxide coating by plasma-enhanced chemical vapor deposition (PECVD) can improve the abrasion resistance of polycarbonate, qualifying it for glazing applications. However, the prior PECVD technology using silane and nitrous oxide as the precursors was slow and therefore uneconomical, having a typical deposition rates of only about 0.05 microns per minute. Organosilicon precursors were later used in PECVD for a plasma-generated abrasion-resistant polymer coating, but the deposition rate was not significantly improved.
The process of this invention provides coatings and layers which impart improved adhesion, thermal expansion compatibility, radiation protection, or abrasion resistance to articles or products made by the deposition process of the invention. The deposition of such protective coatings by plasma on high and low temperature materials in the form of sheets, films, and shaped substrates can be achieved by the apparatus and methods disclosed herein.